1. Field of the Invention
The present invention relates to a porphyrin-based compound, a dye including the same and a dye-sensitized solar cell, and more particularly, to a dye for a dye-sensitized solar cell, having improved photoelectric conversion efficiency, and to a dye-sensitized solar cell including the same.
2. Description of the Related Art
A solar cell for converting light energy into electric energy using a photovoltaic effect is an eco-friendly energy source using infinite resources, unlike the other energy sources. It is known to be a silicon solar cell, a dye-sensitized solar cell, etc.
A silicon solar cell is manufactured at very high cost and is thus difficult to actually use, and its efficiency is also difficult to improve. On the other hand, because a dye-sensitized solar cell is much lower in manufacturing cost than the conventional silicon solar cell, it has the potential to replace the conventional amorphous silicon solar cell. The dye-sensitized solar cell has a mechanism of absorbing visible light energy to thus produce electron-hole pairs, and is a photoelectrochemical solar cell composed mainly of a transition metal oxide for transferring produced electrons and a photosensitive dye molecule.
Currently useful as a dye for a dye-sensitized solar cell, a ruthenium complex exhibits an energy conversion efficiency of more than 10% and thereby has received academic attention, but has not yet been commercialized due to low stability which is a major problem concerning the complex-based dye.
To overcome such a problem, novel organic compounds are being studied as the dye. Especially, thorough research into using, as a dye, a porphyrin compound well-known to be a photosynthesis material, has been carried out, but its efficiency is about 1 to 3% which is not high. Hence, the Durrant research team of Imperial College in the UK reported that the reason why the efficiency of the porphyrin dye is lower than that of the ruthenium complex is that the porphyrin dye in an excited state is converted into a ground state by dipole-dipole attraction between adjacent porphyrin compounds.
Meanwhile, Japanese Patent Publication Application No. 2002-063949 (2002 Feb. 28) discloses a porphyrin derivative having photoelectric conversion properties, wherein phenyl groups are substituted at 5, 10, 15 and 20 positions of porphyrin, as represented below. However, such a porphyrin compound suffers from low energy conversion efficiency because of recombination of excited electrons between porphyrin dyes.

(wherein R is a hydrogen atom or an acidic substituent)
Also, Korean Patent No. 10-0809496 discloses a porphyrin derivative configured such that an amine group or an ether group is linked to phenyl groups substituted at 5, 10, 15 and 20 positions of porphyrin in order to extend conjugation, and Korean Patent Publication Application No. 10-2013-0066547 discloses a porphyrin derivative configured such that an amine group is substituted at 5 position of porphyrin and phenyl groups are substituted at 10, 15 and 20 positions of porphyrin.
Although the porphyrin compounds thus disclosed may prevent recombination between dyes compared to the porphyrin derivative of Japanese Patent Publication Application No. 2002-063949, only a single electron acceptor may be provided, making it difficult to increase adsorption of dye on the surface of TiO2, consequently showing low energy conversion efficiency.
Therefore, there is a need to develop a porphyrin derivative for a dye-sensitized solar cell, having superior long-term stability compared to a ruthenium complex and superior photoelectric conversion efficiency compared to conventional porphyrin dyes.